DE102019134200A1 - Pipetting unit with capacitive liquid detection, combination of such a pipetting unit and a pipette tip, and method for capacitive detection of pipetting liquid - Google Patents

Abstract

A pipetting unit (2) with capacitive liquid detection comprises: a pressure tube (10); a shield (12) disposed around the pressure tube (10); a coupling (14) for temporarily attaching a pipette tip (4) to the pipette unit (2), there being an electrical connection between the pressure tube (10) and the pipette tip (4) when the pipette tip (4) is connected; and an electrical circuit (20) which is coupled to the pressure pipe (10) and the shield (12), the electrical circuit (20) being set up to apply a time-variable electrical signal to the pressure pipe (10) via which at connected pipette tip (4) a capacitive detection of a contact between the pipette tip (4) and the pipetting liquid (112) is possible, and the electrical circuit (20) is set up to connect the shield (12) to ground.

Description

The present invention is in the field of pipetting systems and their components. In particular, the present invention relates to pipetting systems in which pipetting liquid is aspirated or dispensed and in which the contact between the pipette tip and the pipetting liquid can be detected.

Modern pipetting systems are highly complex technical systems. They are designed to aspirate and dispense very small amounts of pipetting liquid at high speed and with high accuracy. A large number of pipette tips are often arranged in a Rastar in order to be able to carry out a large number of pipetting operations at the same time. In order to achieve a high level of accuracy, attempts have been made in the past to detect the fill level of the pipetting liquid in a container and to match the pipetting operation to the fill level in the container from which it is to be aspirated or into which it is to be dispensed. However, the previous approaches have not been satisfactory in every respect.

Accordingly, it would be desirable to provide a pipetting unit with liquid detection and a method for detecting pipetting liquid which enable effective and reliable detection of the pipetting liquid.

Exemplary embodiments of the invention include a pipetting unit with capacitive liquid detection, comprising a pressure tube; a shield disposed around the pressure pipe; a coupling for temporarily attaching a pipette tip to the pipette unit, with an electrical connection between the pressure tube and the pipette tip when the pipette tip is connected; and an electrical circuit which is coupled to the pressure tube and the shield, the electrical circuit being set up to apply a time-variable electrical signal to the pressure tube, via which a capacitive detection of a contact between the pipette tip and the pipette liquid is possible when the pipette tip is connected, and wherein the electrical circuit is configured to ground the shield.

Exemplary embodiments of the invention enable an effective and reliable detection of a contact between the pipette tip and the pipette liquid in the pipette unit. By applying a temporally variable electrical signal to the pressure tube and through the electrical connection between the pressure tube and the pipette tip, an abrupt change in the capacitance between the pipette tip and the liquid to be pipetted, as occurs when the pipette tip touches the pipetting liquid, can be effectively detected. Furthermore, because the shielding arranged around the pressure pipe is connected to ground, it can be achieved that the time-variable electrical signal is available largely free of interference. In particular, the pressure pipe and the shielding can carry the time-varying electrical signal according to the principle of a coaxial cable, whereby a strong decoupling from interfering influences, such as electromagnetic interference from the environment and / or parasitic capacitances, can be achieved. Because the electrical circuit applies the time-varying electrical signal to the pressure pipe as well as providing the ground connection for the shielding, a particularly well-defined signal transmission environment for the time-varying electrical signal and particularly good shielding of the time-varying electrical signal can be achieved become. The capacitive detection of the contact between the pipette tip and the pipette liquid is particularly reliable.

In the pipetting unit, the capacitive liquid detection is carried out by capacitive detection of the contact between the pipette tip and the pipette liquid. With a vertical movement of the pipette tip, as is customary when aspirating or dispensing pipetting liquid, the fill level in a container is detected from which pipetting liquid is to be aspirated or into which pipetting liquid is to be dispensed. A well-defined immersion depth of the pipette tip in the pipetting liquid can be achieved, which in turn can lead to a high accuracy of the aspirated or dispensed liquid volume and / or which minimizes or reduces the contamination of the pipette tip with the liquid into which the pipette tip is immersed low level can reduce. The container with pipetting liquid can be any suitable container for pipetting liquid with which the pipetting unit and the pipetting tip can work. Grounded and / or non-electrically conductive containers are particularly suitable. In the field of laboratory automation, so-called labware is often used, in which a large number of indentations, so-called wells, are provided in carrier-shaped or tray-shaped structures for receiving pipetting liquid.

The pipetting unit has a coupling for temporarily attaching a pipette tip to the pipetting unit. The pipette tip can be a disposable pipette tip. The pipette tip can actually only be used for a single aspiration and dispensing process. But it is also possible that the pipette tip for a plurality of aspiration and Dispensing operations before it is disposed of. The coupling can be designed in such a way that when the pipette tip is connected, an essentially gas-tight connection is created between the pressure tube and the pipette tip. A substantially closed volume of compressed air can thus be formed in the pressure tube and the pipette tip, with the exception of the pipette tip opening. In pipetting systems that control the aspiration or dispensing via compressed air in the pressure tube, the essentially gas-tight connection between the pressure tube and the pipette tip enables highly precise control of the volume of liquid to be aspirated or dispensed.

An electric motor, in particular an electric linear motor, can be connected to the pipetting unit. The electric linear motor can have a movable piston, by means of which pressure changes in the pressure tube and the connected pipette tip for aspirating or dispensing the pipetting liquid can be achieved. The electric motor can be interchangeably connected to the pressure tube or it can be formed integrally with the pressure tube and thus with the pipetting unit. The control of the electric motor can be coupled to the electrical circuit of the pipetting unit, so that the control of the electric motor can carry out the aspiration process or dispensing process as a function of the capacitive detection of the contact between the pipette tip and the pipette liquid.

The electrical circuit is set up to apply a time-varying electrical signal to the pressure pipe and to connect the shield to ground. Both the pressure pipe and the shield are electrically conductive. In this way, the time-varying electrical signal and the ground potential can be applied along the pressure pipe or along the shield. The pressure pipe and the shield are at least partially made of electrically conductive material. It is possible for the pressure pipe and / or the shield to consist entirely or essentially entirely of electrically conductive material.

When the pipette tip is connected, there is an electrical connection between the pressure tube and the pipette tip. In other words, the coupling between the pipette tip and the pipette unit is designed in such a way that when the pipette tip is connected, there is an electrical connection between the pressure tube and the pipette tip. For this purpose, the coupling can be at least partially conductive, so that the electrical connection is via one or more components of the coupling. It is also possible that the coupling is designed in such a way that there is direct contact between the pipette tip and the pressure tube at least at one point, so that there is an electrical connection via this direct contact.

The coupling is designed to temporarily fasten a pipette tip to the pipette unit. The pipette tip is in particular an electrically conductive pipette tip. The time-variable electrical signal can thus be applied to the pipette tip via the pressure tube and the electrical connection between the pressure tube and the pipette tip, in particular along the pipette tip up to the pipette tip opening. In this case, the contact between the pipette tip and the pipette liquid can have a direct, reliably detectable influence on the time-varying electrical signal.

The electrical circuit is set up to apply the time-varying electrical signal to the pressure pipe and to connect the shield to ground. In particular, the electrical circuit can be set up to generate the time-variable electrical signal and to apply it to the pressure pipe. Furthermore, the electrical circuit can be set up to carry out the capacitive detection of the contact between the pipette tip and the pipetting liquid when the time-variable electrical signal is applied to the pressure tube, i.e. during or after the time-variable electrical signal is applied to the pressure tube. For this purpose, the electrical circuit can be set up to detect the electrical behavior of the pressure tube, pipette tip and coupling when the time-varying electrical signal is applied and to deduce from this the presence or absence of contact between the pipette tip and the pipette liquid. Due to the sudden change in the capacitance between the pipette tip and the environment, in particular between the pipette tip and the container filled with the pipette liquid, when the pipette tip and the pipette liquid come into contact, the electrical behavior changes abruptly in response to the time-varying electrical signal. By detecting and analyzing the reaction of the system excited by the time-varying electrical signal, the electrical circuit can detect the contact between the pipette tip and the pipette liquid. The electrical circuit can be designed as an electrical circuit for signal generation and application on the one hand and for signal reception and processing on the other hand.

The electrical circuit is set up to ground the shield. Instead of the term ground, other terms, such as earthing or ground, can also be used. The term mass relates to a fixed potential in the pipetting system. The electrical circuit may have an internal ground terminal coupled to the shield. It is also possible that the electrical circuit is connected to an external ground connection, such as, for example, to a housing of the pipetting system, and provides a coupling between this external ground connection and the shield.

According to a further embodiment, the time-variable electrical signal is a periodic signal. In particular, the time-variable electrical signal can be a sinusoidal time-variable electrical signal. A periodic signal is particularly well suited to excite the system of pressure tube, coupling and pipette tip to an electrical oscillation and to determine the contact between the pipette tip and the pipette liquid from the behavior of the resulting oscillating circuit. The term periodic signal also includes a section-wise periodic signal, for example a time-variable electrical signal, in which sections periodic signal curves alternate with signal pauses. A time-variable electrical signal with stringed together signal sections each with periodic signal curves of different frequencies also falls under the term periodic signal.

According to a further embodiment, the periodic signal has a frequency of between 450 kHz and 700 kHz, in particular a frequency between 500 kHz and 650 kHz.

According to a further embodiment, the electrical circuit is set up to determine a resonance frequency of the excited system when the time-variable electrical signal is applied. The term “when the time-varying electrical signal is applied” encompasses the determination of the resonance frequency during the application of the time-varying electrical signal or after application of the time-varying electrical signal. In the first case, the behavior of the excited system can be observed during a forced oscillation, whereby the resonance frequency can be determined by how well the excited system resonates. In the second case, the system can be excited with a time-varying electrical signal which, for example, can have a frequency close to an expected resonance frequency, wherein the resonance frequency can be determined via a free oscillation of the system after the excitation. Determining the resonance frequency can include determining a value of the resonance frequency. It is also possible that no specific value is determined for the resonance frequency, but rather it is determined in which value range the resonance frequency lies. For example, it can be determined whether the resonance frequency is below or above a predetermined threshold. Such a binary determination of the value range of the resonance frequency allows a comparatively less complex evaluation, but can be sufficient for the binary decision as to whether there is contact between the pipette tip or not. The excited system comprises the pressure tube, the coupling, the pipette tip and, in the event of contact with the pipetting liquid, the pipetting liquid and, if applicable, the container for the pipetting liquid. The capacitances and inductances, in particular the parasitic capacitances and inductances, of the components of the excited system form an oscillating circuit, the resonance frequency of which changes when there is contact between the pipette tip and the pipette liquid. The resonance frequency of the excited system can thus be used to detect the contact between the pipette tip and the pipette liquid. A particularly reliable determination of the resonance frequency of the excited system can be achieved by applying different time-varying electrical signals, in particular time-varying electrical signals with different frequencies.

According to a further embodiment, the electrical circuit is set up to repeatedly or continuously apply the time-variable electrical signal to the pressure tube and to detect the contact between the pipette tip and the pipette liquid on the basis of a change in the resonance frequency of the excited system. Due to the differential consideration of the resonance frequency of the excited system at different points in time, the contact between the pipette tip and the pipette liquid can be detected particularly conveniently. In particular, the potentially complex definition of a threshold for the resonance frequency and the comparison of a specific resonance frequency with the threshold can be dispensed with.

According to an alternative embodiment, the electrical circuit is set up to apply a second, time-variable electrical signal to the shield. In other words, instead of connecting the shield to ground, the electrical circuit can be set up, in addition to applying the time-varying electrical signal to the pressure pipe, to apply a second time-varying electrical signal to the shielding. By means of the second time-variable electrical signal, a very low capacitance can be achieved between the pressure pipe and the shielding and a very undisturbed application of the time-variable electrical signal to the pressure pipe. The time-varying electrical signal which is applied to the pressure pipe is also referred to as the first time-varying electrical signal in the context of the alternative embodiment.

According to a further embodiment, the electrical circuit is set up to apply the first time-varying electrical signal and the second time-varying electrical signal to the pressure pipe or the shield in a synchronized manner. The first and the second variable electrical signal can be applied to the pressure pipe or the shield with a synchronized start. Alternatively / additionally, the first and the second time-variable electrical signal can be synchronized with one another at predetermined points in time in the signal sequence, in particular the first and the second time-variable electrical signal can be periodically synchronized with one another. Due to the synchronized application of the first and the second time-variable electrical signal, particularly good shielding against interfering influences can be achieved.

According to a further embodiment, the second time-variable electrical signal corresponds to the first time-variable electrical signal. In particular, the first time-varying electrical signal and the second time-varying electrical signal can have essentially the same signal shape. For this purpose, the electrical circuit can generate two identical signals or generate one signal and apply this one signal to the pressure pipe or the shielding as a first time-variable electrical signal and as a second time-variable electrical signal. Due to the correspondence of the first time-variable electrical signal and the second time-variable electrical signal, particularly good shielding, in particular shielding in the sense of a coaxial cable, can be achieved.

According to a further embodiment, the first time-varying electrical signal and the second time-varying electrical signal are periodic signals. The frequency of the first time-variable electrical signal and of the second time-variable electrical signal can be between 450 kHz and 700 kHz, in particular between 500 kHz and 650 kHz.

The following features and modifications apply both to the embodiment described first, according to which the electrical circuit is set up to ground the shield, and to the alternative embodiment, according to which the electrical circuit is set up to apply a second time-variable signal to the shield , applicable.

According to a further embodiment, the electrical circuit is set up to apply a voltage profile to the pressure pipe as a time-variable electrical signal. The voltage curve can have any suitable shape. For example, the voltage profile can be sinusoidal or consist of time-spaced voltage pulses. The voltage pulses can in particular be voltage pulses of essentially constant voltage. It is emphasized that the electrical circuit can also be set up to apply a current curve as a time-varying electrical signal to the pressure pipe.

According to a further embodiment, the electrical circuit is set up to receive a time profile of an electrical variable on the pressure tube and to detect a contact between the pipette tip and the pipetting liquid from the time profile of the electrical variable on the pressure tube. The electrical quantity on the pressure pipe is the reaction to the time-varying electrical signal. Due to the sudden change in the capacitance between the pipette tip and the pipette liquid when the pipette tip and the pipette liquid come into contact, the reaction to the time-varying electrical signal is different, depending on whether there is contact or not. The electrical variable can be tapped at any suitable location on the pressure pipe or on a component conductively connected to the pressure pipe. It is also possible to determine the electrical variable at the signal output of the electrical circuit for the electrical signal that changes over time. The electrical variable on the pressure pipe can be, for example, the current that arises in response to the application of a voltage curve. The electrical variable can, for example, also be the voltage on the pressure pipe or on a component that is conductively connected to the pressure pipe, which voltage arises in response to the application of a current curve. Depending on the design of the pressure tube and the pipette tip, the design of the time-varying electrical signal, and the positions for applying the time-varying electrical signal and for tapping the electrical variable mentioned, decision criteria can be set up as to whether the electrical variable tapped is a contact between Indicates pipette tip and pipette liquid or not.

According to a further embodiment, the electrical circuit is set up to analyze the time profile of the electrical variable with regard to amplitude and / or slope and / or integral and / or frequency and / or phase and to detect contact between the pipette tip and the pipetting liquid based thereon. A change in amplitude and / or slope and / or integral and / or frequency and / or phase can indicate a change in the capacitance between the pipette tip and the pipette liquid and can thus be interpreted as the occurrence or absence of contact between the pipette tip and the pipette liquid. For the Detection, simple limit values for amplitude and / or slope and / or integral and / or frequency and / or phase can be used. However, it is also possible to apply more complex signal processing to the temporal progression of the electrical variable and to use this to detect the contact.

According to a further embodiment, the electrical circuit is designed in the form of an integral circuit component. The term integral circuit component does not necessarily mean that the electrical circuit is in the form of an integrated circuit (IC) in the narrow sense. Rather, the term integral circuit component is to be understood in such a way that the electrical circuit is present as a coherent, individual component or as a coherent, individual assembly and in particular is designed in a manner that allows the electrical circuit as a whole to be connected to the pipetting unit assemble or remove from this. The electrical circuit can be designed as a single circuit component, and in special designs can also be present as an integrated circuit in the narrower sense.

The electrical circuit can thus be easily assembled, disassembled and replaced.

According to a further embodiment, the electrical circuit is designed as a circuit with printed conductor tracks. In technical jargon, the circuit with printed conductor tracks is also referred to as a printed circuit. In this way, the electric circuit can be produced with a very small size, high accuracy, and high reliability.

According to a further embodiment, the electrical circuit is designed as a flexprint, in particular as a multi-layer flexprint. The term flexprint describes a circuit with printed conductor tracks that is not applied to a rigid plate, but rather has mechanical flexibility. For example, the printed conductor tracks can be introduced into a flexible, rubber-like carrier. The term flexprint can denote a flexible printed circuit. Especially in the field of laboratory automation, the components of pipetting systems move extremely frequently and extremely quickly, both in relation to the pipetting liquid and relative to one another, e.g. when connecting and ejecting a pipette tip. Because it is designed as a flexprint, the electrical circuit can effectively provide the variable electrical signal and thereby enable a high degree of flexibility for the highly compact assembly of the pipetting system. The flexprint can be arranged particularly well in such a way that it does not interfere with the frequent and rapid movements of the components despite the high integration density of the pipetting system.

According to a further embodiment, the electrical circuit is fixed to the pipetting unit with a screw. Furthermore, the electrical circuit can be electrically coupled to the pressure pipe via the screw. Thus, both the mechanical fixing of the electrical circuit and the electrical coupling to the pressure pipe can take place via one component. The screw can provide the double function of mechanical fixing of the electrical circuit on the one hand and the electrical coupling between the electrical circuit and the pressure pipe on the other hand. It is possible to use a screw provided for mechanical fixation in addition for the electrical coupling between the electrical circuit and the pressure pipe. In this way, a separate electrical connection between the electrical circuit and the pressure pipe, which may be prone to errors due to the high integration density, can be avoided.

According to a further embodiment, the electrical circuit is coupled to the pressure pipe via the screw and a threaded hole or via the screw and a screw nut. In other words, the time-varying electrical signal can be applied to the pressure pipe via the screw and a threaded hole or via the screw and a screw nut. For this purpose, there can be a permanent electrical connection between the threaded hole and the pressure tube or the screw nut and the pressure tube, which can be achieved with less complexity and high reliability in terms of manufacturing technology.

According to a further embodiment, the electrical circuit is connected to the pressure tube at an end region of the pressure tube that is remote from the pipette tip. In this way, the pressure pipe and the shield can be provided over a great length as a structural unit with a small cross-sectional dimension. A large integration density of pipetting units can be achieved in pipetting systems with a large number of pipetting units, with sufficient space being available for coupling or uncoupling of pipette tips.

According to a further embodiment, the shield is movably mounted with respect to the pressure pipe. In particular, the shield can be movable to exert an ejection force on a connected pipette tip. In this way, the shield can perform the double function of an electrical shield for the time-varying electrical signal on the pressure tube and a mechanical component designed for uncoupling a pipette tip. The The shield can be arranged coaxially with the pressure pipe, with corresponding bearings enabling a linear movement of the shield with respect to the pressure pipe.

According to a further embodiment, the pipetting unit furthermore has an ejection spring which is arranged on an end region of the shield remote from the pipette tip. In particular, the electrical circuit can be electrically coupled to the shield via the ejection spring. In other words, the electrical circuit can connect the shield to ground via the ejection spring. In this way, the ejection spring can take on the double function of exerting a motive force on the shield on the one hand and the electrical coupling of the electrical circuit and shield on the other hand.

According to a further embodiment, the ejection spring is arranged coaxially around the pressure pipe. In this way, the ejection spring can, on the one hand, apply a rotating force to move the shield. On the other hand, the ejection spring can form an effective part of the shielding of the pressure tube and thus contribute to the fact that the time-varying electrical signal can be used to a large extent undisturbed for the detection of the contact between the pipette tip and the pipette liquid.

According to a further embodiment, the pipetting unit has a plurality of ejection springs, in particular two, three or four ejection springs, which are arranged on an end region of the shield remote from the pipette tip. In this case, the electrical circuit can be electrically coupled to the shield via one or more or all of the plurality of ejector springs. The plurality of ejection springs can be arranged around the pressure pipe, in particular arranged around the pressure pipe at regular radial distances from one another. Instead of a circulating force for moving the shield, the plurality of ejection springs then apply the force for moving the shield in regions that are spaced apart from one another.

According to a further embodiment, the ejection spring or the ejection springs are made of steel, in particular of stainless steel, further in particular of chromium steel. With these materials, the two functions of applying the mechanical motive force and the electrical connection can be achieved particularly well.

According to a further embodiment, the pipetting unit has an insulation which is arranged on an end region of the shield facing the pipette tip. In particular, the insulation can be arranged between the shield and the coupling and / or between the shield and a connected pipette tip. Thus, the time-varying electrical signal and the ground potential at the end region of the shield facing the pipette tip can be effectively separated from one another.

According to a further embodiment, the shield is arranged coaxially to the pressure pipe. In this way, a particularly compact design as well as a particularly effective shielding of the time-varying electrical signal from the interfering influences from the environment is possible. The shield can be of essentially the same length as the pressure pipe.

It is also possible for the pressure tube to protrude from the shield at the end remote from the pipette tip and / or at the end facing the pipette tip.

According to a further embodiment, the coupling is an active coupling for fixing or releasing a pipette tip. In other words, the coupling can be an active coupling for coupling or uncoupling a pipette tip. The active coupling can in particular be a coupling driven by a lifting magnet. The coupling can have control surfaces for fixing / releasing pipette tips. The control surfaces can have a force on moving parts of the coupling, such as moving balls or a moving O-ring. The control surfaces can be moved by the lifting magnet if the coupling is a lifting magnet-driven coupling. The radial position of the balls or the O-ring can be changed by means of the control surfaces so that a pipette tip can be held in position. By moving the balls or the O-ring radially inward, a mechanical fixation of the pipette tip can be canceled so that the pipette tip can be uncoupled. The uncoupling can then take place via a separate mechanism, for example via the interaction of the ejection spring described above and the shield.

According to a further embodiment, the pipetting unit furthermore has a linear motor which is connected to the pressure tube, a piston being movably arranged in the linear motor and pressure changes in the pressure tube for aspirating or dispensing pipetting liquid being possible through movement of the piston.

The linear motor can in particular be a linear electric motor. In particular, the piston can be equipped with permanent magnets, and there can be a plurality of electromagnets be arranged around the path of movement of the piston. By suitably controlling the electromagnets, the piston can be moved in the linear motor and cause desired pressure changes in the pressure pipe. The linear motor can be permanently installed and connected to the pressure pipe. It is also possible that the linear motor is designed as an integrated assembly and can be exchanged as a whole.

Exemplary embodiments of the invention further comprise a combination of a pipetting unit and a pipetting tip, the combination having a pipetting unit according to one of the embodiments described above and having a conductive pipetting tip which can be attached to the pipetting unit. The additional features, modifications and technical effects that have been described above for the pipetting unit apply analogously to the combinations of the pipetting unit with a pipetting tip. The pipetting unit and the conductive pipetting tip can be provided as a kit. It is also possible for the pipetting unit to be installed as part of a pipetting system and for a conductive pipette tip or a supply of conductive pipette tips to be provided separately. Exemplary embodiments of the invention also include the combination of the pipetting unit and the pipetting tip, the conductive pipetting tip being attached to the pipetting unit.

According to a further embodiment, the pipette tip is a disposable pipette tip. The term disposable pipette tip describes a pipette tip that has a much shorter service life than the pipette unit. In particular, the term disposable pipette tip can denote a pipette tip that is generally only used for an aspiration and dispensing process. It is also possible, however, for the disposable pipette tip to be used for a small number of aspiration and dispensing processes, for example for a maximum of ten, in particular a maximum of five, aspiration and dispensing processes. In this way, in laboratory automation, contamination of the samples through contamination of the pipette tip can be avoided or at least kept to a minimum.

According to a further embodiment, the pipette tip is made of conductive polymer material. The manufacture from conductive polymer material enables the time-varying electrical signal to be applied to the pipette tip opening, with the pipette tip being able to be manufactured at a reasonable cost. In particular, such a production makes it possible to use it as a disposable pipette tip in a justifiable manner.

Exemplary embodiments of the invention further comprise a pipetting system having at least one pipetting unit according to one of the embodiments described above. In particular, the pipetting system can have a plurality of pipetting units, each of which is designed according to one of the embodiments described above. The additional features, modifications and technical effects that have been described above for the pipetting unit apply analogously to the pipetting system. The pipetting system can in particular have 96 pipetting units, each of which is designed according to one of the embodiments described above. In this way, the pipetting system can work quickly and effectively with containers commonly used in laboratory automation, which are designed in an 8x12 grid. Other numbers of pipetting units are also possible, in particular other numbers that are well suited to existing grid dimensions.

Exemplary embodiments of the invention further include a method for capacitive detection of pipetting liquid by a pipetting unit, comprising applying a time-varying electrical signal to a pressure tube of the pipetting unit, from which the time-varying electrical signal is applied via a coupling to a pipette tip; Providing a ground connection for a shielding of the pipetting unit, which is arranged around the pressure tube, the time-variable electrical signal and the ground connection being provided by a common electrical circuit; and detecting a contact between the pipette tip and the pipette liquid by means of the time-varying electrical signal. The additional features, modifications and technical effects that have been described above with reference to the pipetting unit apply analogously to the method for capacitive detection of pipetting liquid by a pipetting unit.

According to a further embodiment, the time-variable electrical signal is a periodic signal.

According to a further embodiment, the method further comprises: determining a resonance frequency of the excited system when the time-varying electrical signal is applied.

According to a further embodiment, the method further comprises: repeated or continuous application of the time-varying electrical signal to the pressure tube and detection of the contact between the pipette tip and the pipette liquid on the basis of a change in the resonance frequency of the excited system.

According to a further embodiment, the application of the time-variable electrical signal includes the application of a voltage curve to the pressure pipe.

According to a further embodiment, the method further comprises: receiving or measuring or recording a time profile of an electrical variable on the pressure pipe. The step of detecting the contact between the pipette tip and the pipette liquid can be carried out by means of the time-variable electrical signal and the time profile of the electrical variable on the pressure tube.

According to a further embodiment, the method further comprises: analyzing the time profile of the electrical variable with regard to amplitude and / or slope and / or integral and / or frequency and / or phase and, based on this, detecting the contact between the pipette tip and the pipetting liquid.

According to a further embodiment, the application of the time-varying electrical signal includes applying the time-varying electrical signal to a screw with which an electrical circuit from which the time-varying electrical signal originates is fixed to the pipetting unit and which is electrically connected to the pressure tube is coupled. In particular, the screw can be electrically coupled to the pressure tube via a threaded hole or a screw nut.

According to a further embodiment, providing a ground connection for the shield includes providing a ground connection for an ejection spring, which is electrically coupled to the shield and through which the shield can be moved relative to the pressure pipe.

Exemplary embodiments of the invention further comprise a computer program or a computer program product which contains program instructions which, when executed on a data processing system, carry out a method according to one of the embodiments described above. The individual steps of the method can be initiated by the program instructions and performed by other components or carried out in the data processing system itself.

• 1 zeigt eine Pipettiereinheit gemäß einer beispielhaften Ausführungsform der Erfindung in einem Längsschnitt;
• 2 zeigt die Pipettiereinheit der 1 in einer Seitenansicht;
• 3 zeigt ein Pipettiersystem gemäß einer beispielhaften Ausführungsform der Erfindung in einem Längsschnitt;
• 4 zeigt einen Elektromotor in einem Längsschnitt, wie er in einer Pipettiereinheit gemäß einer beispielhaften Ausführungsform der Erfindung verwendet werden kann.

Further exemplary embodiments of the invention are described below with reference to the accompanying figures.

• 1 shows a pipetting unit according to an exemplary embodiment of the invention in a longitudinal section;
• 2 shows the pipetting unit of 1 in a side view;
• 3 shows a pipetting system according to an exemplary embodiment of the invention in a longitudinal section;
• 4th shows an electric motor in a longitudinal section, as it can be used in a pipetting unit according to an exemplary embodiment of the invention.

1 shows a pipetting unit 2 according to an exemplary embodiment of the invention in a longitudinal sectional view. On the pipetting unit 2 is a pipette tip 4th attached. The pipette tip 4th can be connected to the pipetting unit 2 are coupled and uncoupled from this, as described in detail below. So you can also say that 1 a combination of a pipetting unit 2 and a pipette tip 4th shows.

The pipetting unit 2 has a pressure pipe 10 on. The pressure pipe 10 is rigid with a holder 22nd connected. In particular, the pressure pipe 10 in a corresponding receptacle of the holder 22nd inserted, in particular pressed in. By the holder 22nd extends a pressure line 23 which are in fluid communication with the pressure pipe 10 stands. In the alignment of 1 , which is the operating position of the pipetting unit 2 corresponds, the pressure pipe extends 10 from the holder 22nd downward. At the end of the holder remote from the pressure pipe 22nd instructs the holder 22nd a motor connection 24 to which an electric motor to change the pressure in the pressure line 23 and the pressure pipe 10 is connectable. The motor connection and the electric motor are described below with reference to FIG 3 and 4th described.

The pipetting unit 2 furthermore has a shield 12th on, which is coaxial around the pressure pipe 10 is arranged around. The length of the shield 12th is less than the length of the pressure pipe 10 . The pressure pipe protrudes upwards 10 from the shield 12th out and extends into the holder 22nd , as described above. The pressure pipe protrudes downwards 10 from the shield 12th and forms a holder for the pipette tip 4th as described below. Even if the shield 12th overall is significantly shorter than the pressure pipe 10 , the shield extends 12th over much of the length of the portion of the pressure pipe 10 that came out of the holder 22nd protrudes.

The shield 12th is in the longitudinal direction opposite the pressure pipe 10 movable. Between the shield 12th and the holder 22nd is a drop pen 30th arranged. The drop pen 30th practice one Force on the shield 12th from which the shield 12th relative to the pressure pipe 10 and the holder 22nd wants to move and what the shielding 12th down to eject the pipette tip 4th wants to move. Thus the shield exercises 12th in consequence of the by the pen 30th force exerted an ejection force on the pipette tip 4th out. The ejection mechanism is described in detail below. The drop pen 30th is coaxial around the pressure pipe 10 arranged around. The drop pen 30th can in particular between a lower end face of the holder 22nd and a top face of the shield 12th be arranged to effectively apply the spring force to the shield 12th transferred to. Instead of the one, coaxially around the pressure pipe 10 drop spring arranged around it 30th can also have a plurality of ejection springs around the pressure pipe 10 be arranged around. The individual ejection springs of this plurality of ejection springs are smaller in cross section than those coaxially around the pressure tube 10 ejector spring arranged around it 30th . For example, in the longitudinal sectional view of 1 right and left of the pressure pipe 10 be arranged in each case an ejection spring.

The shield 12th can be an injection molded part. It can consist, for example, of a chrome-coated nickel-copper-nickel arrangement, and the outer surfaces can be lacquered for insulation. The drop pen 30th or the ejection springs can be made of chrome steel, for example.

The pipetting unit 2 still has a coupling 14th on. The coupling 14th enables the temporary attachment of the pipette tip 4th on the pipetting unit 2 . In particular, the coupling enables 14th that the pipette tip 4th so on the pipetting unit 2 that can be attached to the pipette tip 4th opposite the pressure pipe 10 is immobile. The coupling 14th has a positioning element 16 and a plurality of balls 18th on which around the pressure pipe 10 are arranged around in a cage. The cage allows the balls to move radially 18th within predetermined limits and prevents free movement of the balls 18th . The positioning element 16 has a downward-facing contact surface with which a step along the inner surface of the pipette tip 4th is engaged when the pipette tip 4th on the pipetting unit 2 is attached. Through the interaction of the contact surface of the positioning element 16 and the step on the inner surface of the pipette tip 4th becomes the pipette tip 4th when attaching to the pipetting unit 2 brought into a well-defined position in the longitudinal direction, ie in a well-defined position in the top-bottom direction.

The balls 18th are part of a locking mechanism to fix the pipette tip 4th on the pipetting unit 2 . When the pipette tip 4th is brought into the correct longitudinal position, a radially outwardly directed force is applied to the balls via suitable control surfaces 18th applied so that the balls 18th radially outwards into corresponding recesses in the pipette tip 4th move. The control surfaces continue to cause the balls 18th cannot move back radially inward. So is the pipette tip 4th on the pipetting unit 2 secured, and those from the shield 12th by means of the ejection spring 30th applied ejection force can be applied by the pipette tip 4th don't throw off. The pipette tip 4th remains firmly on the pipetting unit 2 without having to be held in this position from the outside.

When the pipette tip 4th should be removed, the control surfaces are moved so that they hit the balls 18th the coupling 14th release to the extent that they can move radially inward. The ones through the shield 12th applied ejection force pushes the pipette tip 4th downwards and decouples it from the pressure pipe 10 .

The pipette tip 4th has a pipette tip opening 40 . When the pipette tip 4th on the pipetting unit 2 is connected, arises in the pipette tip 4th , the pressure pipe 10 , the pressure line 23 and the connected electric motor a volume of compressed air. This volume of compressed air is with the exception of the pipette tip opening 40 completed. By changing the pressure in the compressed air volume by means of the connected electric motor, pipetting liquid can pass through the pipette tip opening 40 aspirated or dispensed.

The pressure pipe 10 who have favourited shielding 12th , the positioning element 16 and the pipette tip 4th are electrically conductive. At the end of the shield facing the pipette tip 12th is an isolation 32 provided, which when the pipette tip is connected 4th between the shield 12th and the pipette tip 4th is positioned. Thus there is no electrical connection between the shield 12th on one side and the pressure pipe 10 , the coupling 14th and the pipette tip 4th on the other hand. The pressure pipe 10 is with the attached pipette tip 4th about the coupling 14th electrically connected. In the exemplary embodiment of 1 are both the positioning element 16 as well as the balls 18th electrically conductive.

The pipetting unit 2 furthermore has an electrical circuit 20th on. The electrical circuit 20th has a first part 20A that on the holder 22nd is arranged, and a second part 20B that differed from the holder 22nd extends away. In this way the electrical circuit can 20th convenient electrical signals to the pressure pipe 10 and the shield 12th as described below, and on the other hand conveniently a connection to other components, such as a power supply and a motor controller. The two parts 20A , 20B the electrical circuit 20th are designed as a one-piece assembly that is attached as a whole to the holder 22nd can be attached or can be removed from this. In particular, the electrical circuit 20th be designed as a flexprint. In this way, the comparatively complex geometric arrangement of the electrical circuit 20th are made possible, with the inherent flexibility also in the attachment of the electrical circuit 20th on the holder 22nd and when integrating the pipetting unit 2 is beneficial in a pipetting system.

The electrical circuit 20th is through a screw 26th and a threaded hole 28 on the holder 22nd attached. The threaded hole 28 is in contact with the pressure pipe 10 so that an electrical connection between threaded hole 28 and pressure pipe 10 consists. Even between the screw 26th and the threaded hole 28 there is an electrical connection through the mechanical contact.

The electrical circuit 20th has an electrical connection to the screw 26th . Furthermore, the electrical circuit has 20th an electrical connection to the ejection spring 30th . Accordingly, the electrical circuit 20th an electrical signal or an electrical potential to the screw 26th and the drop spring 30th submit or invest.

The electrical circuit is in operation during operation 20th a capacitive detection of a contact between the pipette tip 4th and pipetting liquid through. In other words, the electrical circuit 20th monitors during operation whether there is contact between the pipette tip 4th and pipetting liquid is present or not. For this purpose there is the electrical circuit 20th a time-varying electrical signal to the screw 26th out. It also sets the electrical circuit 20th a ground potential to the ejection spring 30th at. By placing it on the screw 26th the time-varying electrical signal is also sent to the threaded hole 28 , the pressure pipe 10 who have favourited coupling 14th and the pipette tip 4th created. By applying a ground potential to the drop spring 30th is also the shield 12th on mass.

In the exemplary embodiment of 1 is the time-varying electrical signal generated by the electrical circuit 20th to the screw 26th is applied, a periodic voltage curve or a voltage curve with periodic signal sections. According to the principle of a coaxial cable, the ground potential on the shield shields 12th the time-varying electrical signal. In particular, interference, such as parasitic capacitances between the shielding, can occur 12th and the surroundings of the pipetting unit 2 , from the pressure pipe 10 be held. The influence of interference on the entire system excited by the time-varying electrical signal can also be kept low.

Instead of the ground potential, a second, time-variable electrical signal from the electrical circuit can also be used 20th about the ejection spring 30th to the shield 12th be created. The first time-variable electrical signal, ie the one to the pressure pipe 10 applied time-variable electrical signal, and the second time-variable electrical signal be periodic voltage curves or voltage curves with periodic signal sections. In particular, the first time-varying electrical signal and the second time-varying electrical signal can be synchronized to the screw 26th and the drop spring 30th be created. Furthermore, the first time-variable electrical signal and the second time-variable electrical signal can be corresponding electrical signals which have the same signal shape.

In this way, there are corresponding electrical signals on the pressure pipe 10 and the components around it, shielding 12th and drop spring 30th at. A possible adverse influence of a capacity between pressure pipe 10 and shielding 12th can thus be kept particularly low.

The one described above, attached to the screw 26th applied time-variable electrical signal is up to the pipette tip 4th at, with the components screw 26th , Threaded hole 28 , Pressure pipe 10 and coupling 14th can be used as signal transmission components. The ground potential described above is on the shield 12th on, where the component ejector spring 30th is used as an electrical connection component. The electrical circuit 20th can therefore be connected to components located in the immediate vicinity and use them to apply the time-varying electrical signal and the ground potential. The electrical circuit 20th As a single component, it can ensure that the time-varying electrical signal and the time-varying electrical signal and ground on the pressure pipe are generated 10 and shielding 12th provide. The electrical circuit can be designed as an integral circuit component and can be made compact.

For detecting the contact between the pipette tip 4th and the pipetting liquid observes the electrical circuit 20th the behavior of the pipetting unit 2 and the pipette tip connected to it 4th in response to application of the time varying electrical signal. When applying a periodic voltage curve to the screw as described above 26th can the electrical circuit 20th record and evaluate the current flow occurring in response to this voltage curve. From the relationship between the applied voltage and the resulting current flow, conclusions can be drawn about the electrical properties of the components excited by the signal and their surroundings. For example, the ratio of voltage and current can be an indicator of the inductances and capacitances that screw along the signal transmission path 26th , Threaded hole 28 , Pressure pipe 10 , Coupling 14th and pipette tip 4th are available. In particular, it is possible to draw conclusions about the resonance frequency of the excited system from the ratio of voltage and current. From the amplitude and / or phase offset of the current in relation to the voltage, it can be inferred how well the excited system resonates with the periodic voltage curve. A forced oscillation of the excited system can be observed via the current while the periodic voltage curve is being applied. It makes a big difference for the capacity of the excited system, ie for the capacity of the excited resonant circuit, whether the pipette tip 4th is immersed in a pipetting liquid or hangs freely in the air. Immersing the pipette tip 4th into a pipetting liquid is accompanied by a jump in capacity. By analyzing the current flow when applying the periodic voltage curve, the electrical circuit 20th detect such a jump in capacity. In particular, the electrical circuit can determine from the amplitude and / or the slope and / or the integral and / or the frequency and / or the phase offset of the current flow whether there has been a significant change in the capacitance. Such a significant change can be seen as immersion of the pipette tip 4th into the pipetting liquid or as pulling out the pipette tip 4th can be evaluated from the pipetting liquid. This information can be used by the electrical circuit 20th to the control of the electric motor of the pipetting unit 2 so that the aspiration or dispensing of pipetting liquid can always take place at a defined depth of immersion in the pipetting liquid.

Instead of the described forced oscillation of the excited system, it is also possible to excite the system in a first step with the time-variable electrical signal, in particular with a periodic, time-variable electrical signal, and in a second step after the excitation has ended, a free oscillation of the excited system System to analyze. For example, in the first step of the electrical circuit 20th a periodic stress curve on the screw 26th be created. In the second step, the electrical circuit 20th Then observe the free oscillation of the excited system using the voltage curve applied to the screw and determine the resonance frequency of the excited system from this.

2 shows the combination of the pipetting unit 2 and the connected pipette tip 4th the 1 in a side view. In particular shows 2 the pipetting unit 2 and the pipette tip 4th in a side view from the left in the plane of the drawing 1 . In the area of the transition between shielding 12th and holder 22nd is the pipetting unit 2 shown partly as a side view and partly cut away. The cut part shows a short section of the pressure pipe 10 free so that the connection of the pressure pipe 10 to the holder 22nd you can see. A small part of the shield 12th , the subsequent ejection spring 30th and a small part of the holder 22nd are accordingly in 2 only half shown. It goes without saying that the ejection spring 30th and the shield 12th the pressure pipe 10 surrounded, also in the area shown cut open.

In 2 it can be seen that the electrical circuit 20th over a large part of the side surface of the holder 22nd extends. Various electrical / electronic components are provided which, for example, perform the tasks of applying the time-varying electrical signal, providing the ground connection, and analyzing the reaction of the pipetting unit 2 and the pipette tip 4th on the time-varying electrical signal, the communication with the control of the electric motor, etc., can meet.

3 shows a pipetting system 100 according to an exemplary embodiment of the invention in a longitudinal section. The pipetting system 100 has a pipetting unit 2 according to an exemplary embodiment of the invention. The pipetting unit 2 of the pipetting system 100 the 3 can the pipetting unit 2 the 1 and 2 but can also have a modified structure. In 3 is still an electric motor 6th as part of the pipetting unit 2 shown above with reference to 1 and 2 has already been hinted at. As in 1 and 2 is the pipetting unit 2 in 3 with a connected pipette tip 4th shown.

Due to the arrangement of the pipetting unit 2 in the pipetting system 100 and use in the pipetting system 100 is the pipetting unit 2 Part of the pipetting system 100 . 3 shows the pipetting unit 2 in the same longitudinal sectional plane as 1 , but mirrored. The pipetting system is accordingly 100 shown in this longitudinal sectional plane.

The pipetting system 100 has a housing 102 on which the pipetting unit 2 is attached. In particular, is the pipetting unit 2 by means of the holder 22nd on the housing 102 attached. The pressure pipe 10 and the shield 12th the pipetting unit 2 stand out of the case 102 emerged. In particular, the pressure pipe protrude 10 and the shield 12th in the plane of the 3 which the operational orientation of the pipetting system 100 corresponds to the bottom of the housing 102 out. The pressure pipe 10 extends from within the housing 102 to the outside of the housing 102 . By attaching the holder 22nd on the housing 102 is the pressure pipe 10 stationary opposite the housing 102 of the pipetting system.

As already mentioned above, the pipetting unit 2 the one related to 1 and 2 have the structure described. But it is also possible that the pipetting unit 2 from which referring to 1 and 2 described structure differs. In particular, is the pipetting unit 2 in the 3 shown so that the pressure pipe 10 through the whole holder 22nd extends and even forms the motor connection. Also is the drop spring 30th in 3 shown so that there is a force between the housing 102 of the pipetting system 100 and the shield 12th exercises. The electrical circuit of the pipetting unit is also in this configuration 2 with the drop spring 30th connected to provide the ground connection.

The pipetting unit 2 the 3 has an electric motor 6th on. The electric motor 6th is above the holder 22nd arranged. The pressure pipe connection of the electric motor 6th which below with reference to 4th is with the motor connection of the holder 22nd or directly with the pressure pipe 10 connected. In the exemplary embodiment of 3 is the electric motor 6th as an integrated assembly, which is integrated as a whole in the housing 102 can be used or out of the housing 102 can be removed. So can the electric motor 6th as part of maintenance of the pipetting system 100 or easily replaced in the event of other problems.

The aspiration or dispensing of a pipetting liquid through the pipette tip 4th takes place via the build-up or decrease of a gas pressure in the compressed air volume that is in the interior of the electric motor 6th , in the pressure pipe 10 and in the pipette tip 4th is formed. The gas pressure is built up or decreased by the movement of a piston in the electric motor, as described below with reference to FIG 4th described.

The control of the build-up or the decrease of the gas pressure can be initiated by a contact between the pipette tip 4th and a pipetting liquid by means of the electrical circuit 20th has been detected. The contact between pipette tip 4th and the pipetting liquid is achieved in that the pipetting unit 2 is moved vertically. During the vertical movement, the above-described detection of the presence or absence of contact between the pipette tip takes place 4th and pipetting liquid instead. Illustrative shows 3 a container 110 , in which pipetting liquid 112 is available. By moving the pipetting unit vertically 2 there may be contact between the pipette tip 4th and pipetting liquid 112 are produced, and by building up or relieving the gas pressure in the pressure pipe 10 by means of the electric motor 6th pipetting liquid can then be aspirated or dispensed.

In 3 is the pipetting system 100 for reasons of clarity with a pipetting unit 2 and a pipette tip 4th shown. It goes without saying that the pipetting system 100 a plurality of pipetting units 2 , each with its own electric motor 6th may have. To each of these multiple pipetting units 2 can use a pipette tip 4th be temporarily attached, ie coupled and uncoupled. For example, 96 pipetting units 2 be provided in a standardized grid in the pipetting system 100 can be arranged. It is also possible that the majority of pipetting units 2 can be individually moved vertically in order to be individually immersed in selected containers with pipetting liquid.

4th shows an electric motor 6th in a longitudinal section which can be used in a pipetting unit according to an exemplary embodiment of the invention. The electric motor 6th the 4th can in the pipetting system 100 the 3 be used. In particular, the electric motor 6th the 4th have the same structure as the electric motor 6th the 3 .

The electric motor 6th has a housing 64 , in which a large number of components are housed. Out of the case 64 stick out a power connector 68 and a guide element 72 out. The guiding element 72 serves the end of the electric motor remote from the pressure pipe 6th to be reliably positioned in the housing of the pipetting system.

In the case 64 is essentially a cylindrical guide tube in the middle 74 arranged. The guide tube 74 ends in an end area facing the pressure pipe 92 in a pressure pipe connection 66 . The pressure pipe connection 66 is in the exemplary embodiment of 4th integral with the guide tube 74 educated. In particular, it forms an end region of the guide tube 74 the pressure pipe connection 66 . In the end area facing away from the pressure pipe 94 is a stop air filter unit 90 intended. The stop air filter unit 90 prevents dust from entering the guide tube 74 and forms the end of the path of movement of one described below in the guide tube 74 arranged piston 76 .

To the guide tube 74 around is a plurality of coils 80 arranged, of which only one is provided with a corresponding reference number. In the exemplary embodiment of 4th are twenty coils 80 available. The spools 80 are circular around the guide tube 74 arranged around. They are adjacent to one another along the guide tube 74 arranged, for example, on one another on the guide tube 74 postponed. The majority of coils 80 is with the power connector 68 connected, the one hand along the coils 80 from the end area facing the pressure pipe 92 up to the end area facing away from the pressure pipe 94 runs and on the other hand from the housing 64 protrudes. The spools 80 are connected to the power supply 68 supplied with energy. They work in the operation of the electric motor 6th as an electromagnet.

In the exemplary embodiment of 4th is in the power connector 68 for each of the coils 80 a conductor track is provided around the coils 80 to be supplied with electricity. It is also possible to use several coils at a time 80 with electricity from a conductor track of the power connection 68 are supplied. In particular, it is possible to have three current phases via the power connection 68 be made available, being attached to each spool 80 one of the three current phases is present.

In the guide tube 74 is a piston 76 arranged. The piston 76 has a seal on its side facing the pressure pipe as well as on its side facing away from the pressure pipe 84 . Through the seals 84 are the volume of air between the piston 76 and the pressure pipe connection 66 on the one hand as well as between the piston 76 and the stop air filter unit 90 on the other hand separated from each other.

The piston 76 has six permanent magnets 78 each the same length along the piston 76 to have. The permanent magnets 78 are each with poles in the same direction to one another in the piston 76 arranged. An exemplary arrangement of the permanent magnets 78 would be SN-NS-SN-NS-SN-NS, where the hyphen denotes the boundary between the individual permanent magnets. In 4th are the boundaries between the permanent magnets 78 marked by double lines. Through the permanent magnets 78 generated by the piston 76 a magnetic field with alternating south and north poles, which are extremely selective due to the arrangement with opposing poles.

In the case 64 is also a plurality of magnetic field sensors 82 arranged. The magnetic field sensors 82 are along the guide tube 74 , outside the plurality of coils 80 and along a wall of the housing 64 arranged. There are a total of twenty magnetic field sensors along the guide tube 74 arranged, where the reference number 82 only appears once for reasons of clarity. The majority of magnetic field sensors 82 are Hall sensors in the present example. You measure this at the respective points on the electric motor 6th prevailing magnetic field. The measured values can be used to determine the position of the piston 76 can be used.

In the case 64 of the electric motor 6th is still a cooling shaft 86 arranged. The cooling shaft 86 is along one wall of the case 64 arranged, on the opposite side, based on the guide tube 74 , compared to the majority of magnetic field sensors 82 . The cooling shaft 86 extends essentially from the end region facing the pressure pipe 92 of the housing 64 to the end area facing away from the pressure pipe 94 of the housing 64 . The cooling shaft 86 has an opening through the housing at both ends 64 so that cooling air from the outside through the cooling duct 86 can flow.

Operation of the electric motor 6th is described below. The majority of coils 80 are connected to the power supply 68 charged with electricity. By applying appropriate currents to the plurality of coils 80 Time-varying magnetic fields are generated, which act on the permanent magnets 78 of the piston 76 exert a mechanical force and this within the guide tube 74 move. It is known to those skilled in the art how to control the flow of current through the plurality of coils 80 must be designed to achieve a desired movement of the piston 76 to achieve. As a result, a more detailed description of the relationships between the movement of the piston 76 and the currents to be applied through the coils 80 be waived.

The majority of magnetic field sensors measure during operation 82 this at the respective points within the housing 64 prevailing magnetic field. They transmit the measured values to a control unit of the electric motor 6th . This control unit is able to use the measured values of the magnetic field sensors 82 the position of the piston 76 to determine. On the basis of this information, on the basis of the information about a contact between the pipette tip and the pipette liquid and on the basis of a desired aspiration or dispensing process, the control unit acts on the plurality of coils 80 via the power connection 68 with appropriate currents so that the desired movement of the piston 76 he follows. Between pistons 76 , Magnetic field sensors 82 , Control unit, power connection 68 , and bobbins 80 can consist of a control loop that allows a highly precise positioning of the piston 76 inside the guide tube 74 enables.

Although the invention has been described with reference to exemplary embodiments, it will be apparent to a person skilled in the art that various changes can be made and equivalents used without departing from the scope of the invention. The invention is not intended to be limited to the specific embodiments described. Rather, it contains all embodiments that fall under the appended claims.

Claims (27)

Pipetting unit (2) with capacitive liquid detection, comprising: a pressure pipe (10); a shield (12) disposed around the pressure tube (10); a coupling (14) for temporarily attaching a pipette tip (4) to the pipette unit (2), there being an electrical connection between the pressure tube (10) and the pipette tip (4) when the pipette tip (4) is connected; and an electrical circuit (20) coupled to the pressure tube (10) and the shield (12), wherein the electrical circuit (20) is set up to apply a time-variable electrical signal to the pressure tube (10), via which a capacitive detection of a contact between the pipette tip (4) and the pipette liquid (112) is possible when the pipette tip (4) is connected, and wherein the electrical circuit (20) is set up to connect the shield (12) to ground. Pipetting unit (2) Claim 1 , wherein the time-varying electrical signal is a periodic signal. Pipetting unit (2) Claim 1 or 2 , wherein the electrical circuit (20) is set up to determine a resonance frequency of the excited system when the time-variable electrical signal is applied. Pipetting unit (2) Claim 3 , wherein the electrical circuit (20) is set up to repeatedly or continuously apply the time-variable electrical signal to the pressure tube and to detect the contact between the pipette tip (4) and the pipette liquid (112) on the basis of a change in the resonance frequency of the excited system. Pipetting unit (2) according to one of the preceding claims, wherein the electrical circuit (20) is set up to apply a voltage curve as a time-variable electrical signal to the pressure tube (10). Pipetting unit (2) according to one of the preceding claims, wherein the electrical circuit (20) is set up to receive a time profile of an electrical variable on the pressure tube (10) and a contact from the time profile of the electrical variable on the pressure tube (10) to be detected between the pipette tip (4) and the pipetting liquid (112). Pipetting unit (2) Claim 6 , wherein the electrical circuit (20) is set up to analyze the time course of the electrical variable with respect to amplitude and / or slope and / or integral and / or frequency and / or phase and based on this, a contact between the pipette tip (4) and the pipette liquid ( 112) to be detected. Pipetting unit (2) according to one of the preceding claims, wherein the electrical circuit (20) is designed in the form of an integral circuit component. Pipetting unit (2) according to one of the preceding claims, wherein the electrical circuit (20) is designed as a circuit with printed conductor tracks. Pipetting unit (2) according to one of the preceding claims, wherein the electrical circuit (20) is designed as a flexprint, in particular as a multi-layer flexprint. Pipetting unit (2) according to one of the preceding claims, wherein the electrical circuit (20) is fixed to the pipetting unit (2) with a screw (26) and wherein the electrical circuit (20) is connected to the pressure tube (10) via the screw (26) ) is coupled. Pipetting unit (2) Claim 11 , wherein the electrical circuit (20) is coupled to the pressure tube via the screw (26) and a threaded hole (28) or a screw nut. Pipetting unit (2) according to one of the preceding claims, wherein the electrical circuit (20) is connected to the pressure tube (10) at an end region of the pressure tube (10) remote from the pipette tip. Pipetting unit (2) according to one of the preceding claims, wherein the shield (12) is movably mounted relative to the pressure tube (10), the shield (12) in particular for Exercise of an ejection force on a connected pipette tip (4) can be moved. Pipetting unit (2) Claim 14 , further comprising an ejection spring (30) which is arranged on an end region of the shield (12) remote from the pipette tip, the electrical circuit (20) being coupled to the shield (12) via the ejection spring (30). Pipetting unit (2) Claim 15 , wherein the ejection spring (30) is arranged coaxially around the pressure tube (10). Pipetting unit (2) Claim 15 or 16 wherein the ejector spring (30) is made of steel, in particular of stainless steel, further in particular of chrome steel. Pipetting unit (2) according to one of the preceding claims, further comprising an insulation (32) which is arranged on an end region of the shield (12) facing the pipette tip, in particular between the shield (12) and the coupling (14) and / or a connected pipette tip (4) is arranged. Pipetting unit (2) according to one of the preceding claims, wherein the shield (12) is arranged coaxially to the pressure tube (10). Pipetting unit (2) according to one of the preceding claims, wherein the coupling (14) is an active coupling, in particular a lifting magnet-driven coupling, for fixing or releasing a pipetting tip (4). Pipetting unit (2) according to one of the preceding claims, further comprising a linear motor (6) which is connected to the pressure tube (10), wherein a piston (76) is movably arranged in the linear motor (6) and wherein by a movement of the piston (76) Changes in pressure in the pressure tube (10) for aspirating or dispensing pipetting liquid (112) are possible. Combination of a pipetting unit (2) and a pipetting tip (4), comprising: a pipetting unit (2) according to one of the preceding claims; and a conductive pipette tip (4) which can be attached to the pipette unit (2). Combination according to Claim 22 , wherein the pipette tip (4) is a disposable pipette tip. Combination according to Claim 22 or 23 , wherein the pipette tip (4) is made of conductive polymer material. Pipetting system (100) comprising a plurality of pipetting units (2), each of which according to one of the Claims 1 to 21 is executed, in particular having 96 pipetting units (2), each of which according to one of the Claims 1 to 21 is executed. A method for capacitive detection of pipetting liquid (112) by a pipetting unit (2), comprising: Applying a time-varying electrical signal to a pressure tube (10) of the pipetting unit (2), from which the time-varying electrical signal is applied to a pipette tip (4) via a coupling (14); Providing a ground connection for a shield (12) of the pipetting unit (2), which is arranged around the pressure tube (10), the time-variable electrical signal and the ground connection being provided by a common electrical circuit (20); and Detecting a contact between the pipette tip (4) and the pipette liquid (112) by means of the time-varying electrical signal. Computer program that contains program instructions that, when executed on a data processing system, follow a method Claim 26 carry out.

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